Servo motors and drives are extremely useful components in machine automation. Unlike standard induction motors, they offer the highest possible accuracy and precision; this is a useful standard for system operation. Point-to-point accuracy cannot be achieved using standard induction motors. Motion control works very well due to closed-loop control. The drive will always require actual encoder counts for PID-type control and to reduce the error between the given output and the actual received output. The discrepancy is continuously corrected by a high-configuration servo drive circuit.
I. Introduction to the Working Principle of Servo Drivers
First, let's look at how a servo driver works.
A servo drive is a controller used to control a servo motor, and its function is similar to that of a frequency converter used in ordinary AC motors. It is part of a servo system and is mainly used in high-precision positioning systems.
Currently, mainstream servo drives all use digital signal processors (DSPs) as their control core, enabling more complex control algorithms and achieving digitalization, networking, and intelligence. Power devices typically use drive circuits centered around intelligent power modules (IPMs). The drive circuitry is integrated into the IPM and includes fault detection and protection circuits for overvoltage, overcurrent, overheating, and undervoltage. A soft-start circuit is also added to the main circuit. To reduce the impact of the startup process on the drive, the power drive unit first rectifies the input three-phase power or mains power through a three-phase full-bridge rectifier circuit to obtain the corresponding DC power. After rectification, the three-phase AC or mains power is driven by a three-phase sinusoidal PWM voltage inverter. The entire process of the power drive unit can be simply described as an AC-DC-AC process.
With the large-scale application of servo systems, the use, debugging, and maintenance of servo drives are important technical issues for servo drives today.
Servo drives are an important component of modern motion control and are widely used in automated equipment. In particular, servo drives for controlling AC permanent magnet synchronous motors have become a research hotspot both domestically and internationally. Vector control-based three-loop control algorithms for current, speed, and position are commonly used in the design of AC servo drives.
Okay, that concludes our explanation of how a servo driver works. Now, let's look at how to control a servo driver.
II. Servo Driver Control Method
There are four control methods for servo drives: feedback-compensated open-loop control, closed-loop control, semi-closed-loop control, and feedback-compensated semi-closed-loop control. Below, we will introduce the first three control methods.
1. Feedback-compensated open-loop control
Open-loop systems have lower accuracy because the stepping error, start/stop error, and mechanical system error of the servo drive directly affect positioning accuracy. This system combines the advantages of both open-loop and closed-loop systems, possessing the stability of open-loop and the accuracy of closed-loop. Due to the machine's resonant frequency, creep, and motion losses, the system will not oscillate. Feedback-compensated open-loop control eliminates the need for backlash compensation and pitch compensation.
2. Closed-loop control
The closed-loop control method not only has a front-end control channel but also a feedback channel for detecting the output. After comparing the command signal with the feedback signal, the deviation signal is obtained to form a closed-loop control system controlled by the deviation.
3. Semi-closed-loop control
For closed-loop control systems, a well-designed system can achieve reliable stability and high precision. However, directly measuring the table position signal requires the use of devices such as gratings, magnetic scales, or linear inductive synchronizers in locations with high installation and maintenance requirements. By measuring the angular displacement of the drive shaft or lead screw, an equivalent feedback signal for the position output can be indirectly obtained. Since the error caused by this part of the transmission mechanism cannot be caused by the closed-loop system excluding the transmission chain from the rotary shaft to the table, the error caused by this part of the transmission mechanism cannot be automatically compensated through closed loop. Therefore, it can be said that it consists of an equivalent feedback signal. The closed-loop control system is a semi-closed-loop servo drive; this control method is called the semi-closed-loop control method.
The above is what I wanted to share with you today about the working principle and control methods of servo drives. I hope you have gained some understanding of the content shared this time.
